Sequence Number Update

ABSTRACT

The invention relates to a method and device in a communications network when a User Equipment, UE, needs to update a next expected Transmission Sequence Number, TSN, continuously in order to avoid discarding successive transmissions. The method comprises: resetting a next expected TSN value in said network and UE to predetermined values after a predetermined inactivity time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/664,373, filed Dec. 11, 2009, which is the National Stage ofInternational Application No. PCT/SE2008/050613, filed May 23, 2008,which claims priority to Swedish Patent Application No. SE 0701488-9,filed Jun. 15, 2007, the disclosures of each of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The invention is related to handling of data transmissions in a wirelesscommunication network. More specifically, it is related to avoiding thediscarding of successive data transmissions between a transmitter and areceiver in a wireless communication network.

BACKGROUND

In wireless communication networks of the latest generation andespecially in HSDPA-based (High Speed Downlink Packet Access) wirelesscommunication networks data sent from a base station towards one or moremobile terminals (UEs) may be scheduled for transmission on high-speedchannels, such as the HS-DSCH (High Speed Downlink Shared Channel).

Also, a UE in these networks may be in different states in a coveragearea serviced by a base station, such as CELL_DCH, CELL_FACH, EnhancedCELL_FACH and other states known to the skilled person.

In the CELL_DCH state, data transmitted on HS-DSCH is grouped intotransport blocks (TBs) each of which among others comprises atransmission sequence number (TSN) in the header portion of the TB andthe user data in the form of MAC-d PDUs (dedicated Media Access ControlPacket Data Units) or MAC-c PDUs (common Media Access Control PacketData Units) in the payload portion. Using a reordering queue as a bufferfor transport blocks received and the TSN from the TB header pluscontrol information sent on a control channel a UE can correctly orderthe TBs received from the base station and forward them to higher layersas MAC-d or MAC-c PDUs. To make the reordering of the TBs moreefficient, each UE has a receiver window having a certain size intowhich TBs with their TSN are received and a timer (T1 timer) whichprevents stalling of the TBs in the reordering queue if some TBs are notcorrectly received.

After a TB is correctly received, the UE updates a parameter indicatingthe TSN for the next expected TB.

This reordering mechanism for the TBs received at the UE is based onindividual (TSNs) and T1 timers, see for example 3GPP TS 25.321.However, when transmitting data on the HS-DSCH using a common H-RNTI, itis not possible to maintain individual TSNs and T1 timers for individualUEs in the network. A single TSN and T1 timer in the network needs to beused for several UEs.

Additionally, in an HSDPA-based wireless network, the Enhanced CELL_FACHstate introduces the reception of data on the HS-DSCH in the CELL_FACHstate and therefore potentially higher data rates. The reception of datain the HS-DSCH in CELL_FACH state is similar to the reception of data inthe HS-DSCH in CELL_DCH state where some of the differences are statedbelow.

A user equipment (UE) in the Enhanced CELL_FACH state receivesretransmissions on HS-DSCH without sending Hybrid Automatic RepeatreQuest (HARQ) feedback signaling (ACK/NACK). Thus, the transportnetwork does not know whether data has been correctly received or not,but rather retransmissions are decided blindly by the network.

Also, the Enhanced CELL_FACH state offers the possibility to transmitdata to UEs using a common HS-DSCH Radio Network Temporary Identifier(H-RNTI). An H-RNTI in an HSDPA network is simply a logical address of aUE in a coverage area of a base station. It is possible that more thanone UE can share one common H-RNTI. This is needed for UEs that haveentered the coverage area of the base station and in the initial HS-DSCHestablishment phase do not have a dedicated H-RNTI assigned yet.

Usually in the Enhanced CELL_FACH state the initial value of the nextexpected TSN is set to 0 in the UE and the discard window is set to[63-WINDOW_SIZE . . . 63], where WINDOW_SIZE refers to the side of thereceiver window. The discard window can be defined as the part of thereceiver window which is not accepted for re-ordering of TBs.

Now, as the network is using a common TSN for all UEs using a commonH-RNTI, there is a likelihood that the first TSN received by the UE iswithin the discard window. In this case the UE will discard the receivedtransmission.

One solution to this problem has been proposed in “Solution toreordering issue in Enhacned Cell_FACH”, 3GPP TSG-RAN WG2#57bis, Kobe,Japan, May 7-11, 2007. It consists of assigning a special initial valueto the next expected TSN, and initializing the discard window based onthe first received TSN. This solution avoids the problem of discardinginitial transmission. However, during continuous reception, it isnecessary for the UE to update the next expected TSN continuously inorder to avoid discarding successive transmissions. This requires thatall (or several) transmitted TSNs are received correctly by the UE. Inpractice the HS-SCCH is power controlled and it may be difficult for theUE to receive all TSNs.

The present invention offers a solution to at least some of the problemsassociated with known technology.

SUMMARY

One aspect of the present invention is related to a method for managingcommunication at a mobile terminal, which may include receiving aninitial transmission unit having a shared destination address andcomprising an initial shared sequence number and a payload carryingdata, determining that the initial transmission unit was correctlyreceived, starting a timer associated with transmission units having acommon destination address and a common sequence number, determiningthat the timer has expired, and resetting the value of sequence numberfor the next expected transmission unit and the upper boundary of areceiver window in the mobile terminal to a predefined initial value.

In this fashion no initial TBs transmitted to a UE which is using shareddestination address (such as a common H-RNTI in HSDPA networks), will bediscarded by the UE. Especially during establishment of a radio channelfor data transmission, where control data may be communicated on theshared destination address between a UE and a base station, data loss isprevented.

Another aspect of the present invention is related to a mobile terminalfor communication in a wireless communication network, where the mobileterminal may include a communication unit for receiving transmissionunits having a shared destination address and comprising a sharedsequence number and payload carrying data, a processing unit configuredfor examining the transmission units received and determining whetherthey are correctly received, a measurement unit comprising a timerassociated with transmission units having a shared destination addressand a shared sequence number where the processing unit is furtherconfigured to instruct the measurement unit to start the timer when aninitial transmission unit with a shared destination address and sharedsequence number is correctly received, the processing unit being furtherconfigured to reset the sequence number for the next expectedtransmission unit and the upper boundary of its receiving window to apredefined initial value upon expiration of the timer.

Yet another aspect of the present invention is related to aninfrastructure node for communication in a wireless communicationnetwork, where the infrastructure node includes a processing unitconfigured for forming transmission units comprising a shared sequencenumber and a payload carrying data to be transmitted to a shareddestination address, a communication unit for transmitting thetransmission units to the shared destination address, a measurement unitcomprising at least one timer associated with transmission units havinga shared destination address and a shared sequence number and where theprocessing unit is configured to instruct the measurement unit to startthe one or more timers upon transmission of an initial transmission unitto a shared destination address, the processing unit being furtherconfigured to reset the sequence number for the next expectedtransmission unit and the upper boundary for the transmission window toa predefined initial value upon expiration of the timer.

Finally, another aspect of the present invention is related to acomputer program for managing communication in a mobile terminal, whichmay include instruction sets for receiving an initial transmission unithaving a shared destination address and comprising an initial sharedsequence number and a payload carrying data, determining that theinitial transmission unit was correctly received, starting a timerassociated with transmission units having a common destination addressand a common sequence number, determining that the timer has expired,and resetting the value of sequence number for the next expectedtransmission unit and the upper boundary of a receiver window in themobile terminal to a predefined initial value.

It may be mentioned that the infrastructure node in the wirelesscommunication network may be a base station, a Node B, an access pointor some other node with the functionality of the infrastructure nodeaccording to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in a non-limiting wayand in more detail with reference to exemplary embodiments illustratedin the enclosed drawings, in which:

FIG. 1 illustrates schematically a flow chart depicting the steps of amethod according to one embodiment of the present invention;

FIG. 2 illustrates in the form of a block diagram a mobile terminalaccording to one embodiment of the present invention,

FIG. 3 illustrates schematically in the form of a block diagram a basestation according to one embodiment of the present invention;

FIG. 4 illustrates schematically the signalling between a base stationand a mobile terminal in a wireless communication network.

DETAILED DESCRIPTION

Before the embodiments of the present invention depicted in FIGS. 1-4are described, some parameters and variables will be defined for betterunderstanding:

Parameter:

-   -   Receiver window size (RECEIVE_WINDOW_SIZE): The        RECEIVE_WINDOW_SIZE is the size of the receiver window according        to the definition below. This is a parameter in the UE and the        value of the parameter is configured by higher layers.

State Variables:

-   -   Next_expected_TSN (next_expected_TSN): The next_expected_TSN is        the Transmission sequence number (TSN) following the TSN of the        last in-sequence reordering PDU received. It may be updated        according to the procedures given. The initial value of        next_expected_TSN=0.    -   Receiver window: The receiver window defines TSNs of those        reordering PDUs that can be received in the receiver without        causing an advancement of the receiver window according to the        procedure below. The size of the receiver window equals        RECEIVE_WINDOW_SIZE and spans TSNs going from        RcvWindow_UpperEdge−RECEIVE_WINDOW_SIZE+1 to RcvWindow_UpperEdge        included.    -   RcvWindow_UpperEdge: The RcvWindow_UpperEdge represents the TSN,        which is at the upper edge of the receiver window. After the        first reordering PDU has been received successfully, it also        corresponds to the reordering PDU with the highest TSN of all        received reordering PDUs. The initial RcvWindow_UpperEdge        equals 63. RcvWindow_UpperEdge is updated based on the reception        of new reordering PDU according to the procedure given below.    -   T1 TSN: The TSN of the latest MAC-ehs SDU that cannot be        delivered to the reassembly entity, when the timer T1 is        started.

Preferably, all state variables are non-negative integers. ReorderingPDUs are numbered by modulo integer Transmission sequence numbers (TSN)cycling through the field 0 to 63. All arithmetic operations, given asexample, on next_expected_TSN, RcvWindow_UpperEdge, T1_TSN and TSN_flushare affected by the 64 modulus. When performing arithmetic comparisonsof state variables or Transmission sequence number values a 64 modulusbase may be used. This modulus base is subtracted (within theappropriate field) from all the values involved and then an absolutecomparison is performed. RcvWindow_UpperEdge−RECEIVE_WINDOW_SIZE+1 maybe assumed to be the modulus base.

Timers:

-   -   Re-ordering release timer (T1): The Re-ordering release timer T1        controls the stall avoidance in the UE reordering buffer as        described below. The value of T1 is configured by upper layers.    -   Reset timer (Treset) (FDD only): Treset controls the reset of        the MAC-ehs reordering functionality when the common H-RNTI is        used.

Turning now to FIG. 1, the method steps of the method according to oneembodiment of the present invention seen from the perspective of a UEare shown. We assume for simplicity that the UE is operating in acoverage area for a base station which in turn has HSDPA functionalityimplemented. However, it should be pointed out that the method accordingto the present invention may be applied in any wireless communicationnetwork where mobile terminals in a coverage area of a base station oraccess point use a shared destination address for data received from thebase station, where data is received in transmission blocks which arenumbered, where the mobile terminals receive these transmission blocksduring a certain receiver window and are able to order the transmissionblocks in the right sequence by means of a reordering mechanism.Therefore, the focus on the HSDPA implementation below should only beregarded as a non-limiting illustrative example.

Also, we assume that the UE has just entered the coverage area of thebase station and does not have a dedicated destination addressallocated, which in the case of the HSDPA network would be a dedicatedH-RNTI, but rather has been allocated a common H-RNTI which it shareswith other UEs present in the same coverage area. We also assume thatthe UE is in the CELL_FACH state, meaning that no HS-DSCH has yet beenestablished between the UE and the base station. This is the startingpoint for the method steps 100-160 which will be described below.

At step 100, the UE initializes the next_expected_TSN parameter to aninitial predefined value which may be 0 for example. Thereafter, the UEstarts at step 110 receiving an initial TB intended for it on a commonH-RNTI, where also each TB has a common TSN. TBs with a common TSN aredelivered to the right individual UE by means of the Queue ID in the TBheader, as is known to the skilled person.

After the reception of the initial TB at the individual UE, the UEchecks at step 120 whether the TB has been received correctly. This maybe checked by methods such as CRC (Cyclic Redundancy Check) or othermethods known to the skilled person and will not be elaborated here.

In case the TB has not been correctly received, the UE stores at step125 the received transport block and proceeds to receive either aretransmission or a new TB at step 110 again. Using HARQ for theHS-DSCH, the UE may then attempt to combine several transmission of thesame TB in order to create a correct TB (step not shown in FIG. 1). Incontrast to solutions suggested by known technology however, no initialTB intended for the UE which just entered the coverage area of the basestation and which is correctly received is discarded if its common TSNlies outside of the UE's receiver window. As mentioned in thedescription of background art, this may happen if there is more than oneUE involved each having their own receiver windows. Instead, at step130, if the UE has determined that the TB has been received correctly,it checks at step 140 whether a timer Treset has been started. If not,the UE starts the Treset timer at step 145. Otherwise, if the Tresettimer is already running it is restarted at step 150. In this fashion, afirst TB which is received at the UE, but which normally would bediscarded if its common TSN would lie outside the receiver window of theUE, will be accepted by UE and therefore data loss will be prevented.Resetting an already running Treset time will ensure that only oneTreset timer is active at a time.

At step 155 the UE stores the correctly received TB in its reorderingqueue. Thereafter, the UE checks at step 160 whether the Treset timerhas expired. If this is not the case, the UE returns to step 110 andcontinues receiving additional TBs. However, if the timer Treset hasexpired, the UE sets at step 170 the next_expected_TSN to an initialvalue again (such as to 0) and the RcvWindow_UpperEdge is set to itsinitial value as well.

The reason for checking whether Treset has expired is that inactivityperiods where no transmission blocks are sent can be detected andtransport blocks with the right initial TSN expected by the UE can bereceived avoiding the loss of the initial transmission as is the casewith some solutions suggested by known technology.

The invention can be applied instead or in addition to the solutionusing a special value for the initial value of the next expected TSN.Moreover the Treset timer in the method illustrated in FIG. 1 may beused in any state where the UE is listening to transmissions on adownlink data or control radio channel where a shared destinationaddress is used.

It should be mentioned that the above described method steps aresuitable to be implemented by a computer program comprising instructionssets running in an internal or external memory of the UE (not shown).

FIG. 2 illustrates an UE 200 according to one embodiment of the presentinvention, where the UE 200 is equipped with a communication unit CMU, amemory MEM, a measurement unit MU, a processing unit CPU and a userinterface UI.

The communication unit CMU may be for example implemented as areceiver/transmitter combination adapted for communication in a wirelesscommunication network, such as a UMTS, HSDPA, HSUPA, LTE or some otherwireless communication network. Even though the description belowfocuses on the implementation of the UE in an HSDPA network, it shouldbe borne in mind that the mobile terminal UE may also function in otherwireless communication networks.

Moreover, the memory MEM may comprise one or more reordering buffers,where transmission blocks are stored in case not all transmission blocksin sequence have yet been delivered, such that they can later be put inthe right order before they are being sent to higher layers fordisassembly into PDUs. This is known to the skilled person.

Also, the memory MEM may be internal, external or a combination of thetwo, where in one part of the memory not comprising the reorderingqueues a computer program may be running which may comprise instructionsets adapted to execute the method steps described in FIG. 1.

Futhermore, the measurement unit MU may comprise at least two timers, ofwhich the first one T1, is known to the skilled person, while the secondTreset is part of the embodiment of the UE according to the presentinvention. The main task of the measurement unit is to start, restartand expire the timers mentioned above by receiving instructions from theprocessing unit CPU to do perform these operations.

Since the function of the timer T1 is sufficiently known to the skilledperson it will not be described further. The function of the Tresettimer on the other hand is, as mentioned earlier, to prevent thediscarding of initially transmitted transport blocks sent to a shareddestination address, such as a common H-RNTI in the HSDPAimplementation.

The processing unit CPU of the UE 200 is adapted to manage functionswhich are known to the skilled person (such as the T1 timer in themeasurement unit MU), but also to instruct the measurement unit to startand restart the Treset timer as well as to set the length Treset timer.Thus the UE 200 according to the present invention may avoid loss ofinitial transmissions during the establishment of the HS-DSCH when theUE 200 enters a coverage area services by a base station. The start ofthe Treset timer may by way of example be performed by sending a triggersignal to the measurement unit MU upon receiving transmission on acommon H-RNTI (if the UE is operating in an HSDPA-network) and a upondetermining that an initial TB has been correctly received. Correctreception of TBs may by way of example be implemented in the processingunit CPU by means of a CRC check, which is known to the skilled person.Those TBs which are correctly received but have a TSN higher than thenext expected TSN may be placed by the processing unit CPU in thereordering buffer in the memory MEM for later in-sequence delivery tohigher layers of the protocol stack.

Additionally, the processing unit may instruct the measurement unit MUto restart the Treset timer if it by examining the state of the Tresettimer detects that the latter is still active and that another TB hasbeen correctly received. In this fashion it is ensured that only oneTreset timer is active in one UE.

Also, the processing unit CPU is adapted to initialize thenext_expected_TSN variable to a predefined initial value, which forexample may be 0 before instructing the measurement unit MU to start theTreset timer.

As another function according to the embodiment of the present inventionin FIG. 2, the processing unit CPU may be adapted to check whether theTreset timer has expired and reset the next_expected_TSN to thepredefined initial value as well as to set theReceiving_Window_UpperEdge to a predefined initial value.

Finally, the UE 200 also comprises a user interface UI for facilitatinginteraction between a user of the UE 200 and the functions provided bythe UE 200 which is well-known to the skilled person.

FIG. 3 illustrates a base station 300 (or a communication gateway)according to one embodiment of the present invention. Even though anHSDPA implementation of the base station 300 is described below, itshould be only regarded as an illustrative example. In fact, the basestation 300 according to the present invention may be used in anywireless communication network as a Node B, base station transceiver,access point or an infrastructure node performing an analogous functionin the network, where data is sent on control and data channels, wheremobile terminals in the coverage area use one common destination addressin the initial channel setup phase and where there is a risk of losingan initial transmission of a transport block due to it being locatedoutside a receiver window of the one or more UEs. Hence, the basestation may be active in such networks as HSDPA, HSUPA (High SpeedUplink Packer Access), 3GPP LTE (Third Generation Partnership ProjectLong Term Evolution) as well as in other wireless communication networksThe base station comprises a communication unit CMU, a processing unitCPU, a memory MEM and a measurement unit MU.

Similar to the function of the communication unit of the UE in FIG. 2,the communication unit CMU comprises a receiver/transmitter combinationfor receiving and transmitting data from and to one or more UEs whichare located in the coverage area of the base station 300. Also, thecommunication unit CMU is adapted for receiving and transmitting datafrom and to an RNC (Radio Network Controller).

The processing unit CPU of the base station 300 is adapted for receivingdata intended for UEs and storing it into buffers of the memory MEM. Inthe HSDPA implementation these buffers may have the function of priorityqueues. Another function of the processing unit CPU is to retrieve datastored from one or more buffers in the memory MEM and to assemble itinto transport blocks. As is known to the skilled person, the processingunit CPU may add a TSN into the header portion of such a transport blockand attach one or more PDUs containing user or control data into thepayload portion of these transport blocks.

Furthermore, the measurement unit MU according to the present inventionmay comprise one or more Treset timers, where each Treset timer isspecific for one UE which is located in the coverage area of the basestation 300. Each time the base station 300 registers a new UE enteringits coverage area not having a dedicated destination address for controldata (such as a dedicated H-RNTI in the HSDPA implementation), theprocessing unit CPU is adapted to initialize the next_expected_TSN to apredefined initial value and to transmit control data on a shareddestination address (for example a common H-RNTI) leading to theestablishment of a high-speed downlink channel. At the same time theprocessing unit CPU instructs the measurement unit MU to start theTreset timer at the start of the transmission of control data to acommon destination address and to increment the next_expected_TSN valueby 1. As is known to the skilled person, the processing unit CPU mayalso initiate retransmissions of transport blocks which in this casewill have a TSN value different from the next_expected_TSN value.

After the processing unit CPU has detected that the Treset timer in themeasurement unit MU has expired the processing unit CPU is adapted toinstruct the measurement unit to restart the Treset timer, thenext_expected_TSN and the transmission window. In this fashion, after aperiod of inactivity, the base station 300 can start sending data againwithout causing initial data loss for UEs that newly entered it's thecoverage area of the base station 300, which would be the case if thenext_expected_TSN was simply incremented further.

Turning now to FIG. 4 an example communication flow between UE and aNode B is schematically represented.

Both the UE and the network implement a reset timer, T_reset. The timeris started (or restarted if it was already running) after eachtransmission using a common H-RNTI, and upon expiring the network andthe UE both will set the next_expected_TSN and the window to theirinitial values (0 or special initial value for TSN).

In the Node B there is one reset timer for each common H-RNTI, wherethese timers may operate independently. In contrast, in the UE there maybe only one reset timer, since the UE may be adapted to only receivedata from the Node B using one common H-RNTI at a time.

The above mentioned and described embodiments are only given as examplesand should not be limiting to the present invention. Other solutions,uses, objectives, and functions within the scope of the invention asclaimed in the below described patent claims should be apparent for theperson skilled in the art.

What is claimed is:
 1. A method for managing communication at a mobileterminal, said method comprising: receiving an initial transmission unithaving a shared destination address and comprising an initial sharedsequence number and a payload carrying data; determining that theinitial transmission unit was correctly received; storing the correctlyreceived initial transmission units in a reordering queue having areordering timer that prevents the stalling of the transmission units inthe reordering queue if some transmission units are not correctlyreceived; starting a reset timer associated with transmission unitshaving a common destination address and a common sequence number;determining that the reset timer has expired; and responsive toexpiration of the reset timer, resetting the value of sequence numberfor the next expected transmission unit and the upper boundary of areceiver window in the mobile terminal to a predefined initial value. 2.The method of claim 1, further comprising restarting the reset timerafter correctly receiving a transmission unit and after determining thatthe reset timer is still running.
 3. The method of claim 1, wherein theinitial transmission unit is received on a control channel with themobile terminal in a state of connecting to a data downlink channel. 4.The method of claim 3, wherein the state comprises an Enhanced CELL_FACHstate.
 5. The method of claim 1, wherein the mobile terminal isoperating in an FDD (Frequency Division Duplex) or TDD (Time DivisionDuplex) wireless communication network.
 6. The method of claim 1,wherein the shared destination address is a common H-RNTI (HS-DSCH RadioNetwork Temporary Identifier).
 7. A mobile terminal for communication ina wireless communication network, comprising: a communication unit forreceiving transmission units having a shared destination address andcomprising a shared sequence number and payload carrying data; aprocessing unit configured for examining the transmission units receivedand determining whether they are correctly received; a measurement unitcomprising a timer associated with transmission units having a shareddestination address and a shared sequence number; and wherein theprocessing unit is further configured to instruct the measurement unitto start the timer when an initial transmission unit with a shareddestination address and shared sequence number is correctly received,and is further configured to reset the sequence number for the nextexpected transmission unit and the upper boundary of its receivingwindow to a predefined initial value upon expiration of the timer.
 8. Amobile terminal in a wireless communication network, comprising: atransceiver for communicating over the wireless communication network; aprocessing unit operatively connected to the transceiver, saidprocessing circuit configured to: receive, via said transceiver, aninitial transmission unit having a shared destination address andcomprising an initial shared sequence number and a payload carryingdata; determine that the initial transmission unit was correctlyreceived; store the correctly received initial transmission units in areordering queue having a reordering timer that prevents the stalling ofthe transmission units in the reordering queue if some transmissionunits are not correctly received; start a reset timer associated withtransmission units having a common destination address and a commonsequence number; determine that the reset timer has expired; andresponsive to expiration of the reset timer, reset the value of sequencenumber for the next expected transmission unit and the upper boundary ofa receiver window in the mobile terminal to a predefined initial value.9. A non-transitory computer-readable medium storing a computer programfor managing communication in a mobile terminal, said computer programcomprising executable program instructions that configure a processingcircuit in a mobile terminal to: receive an initial transmission unithaving a shared destination address and comprising an initial sharedsequence number and a payload carrying data; determine that the initialtransmission unit was correctly received; store the correctly receivedinitial transmission units in a reordering queue having a reorderingtimer that prevents the stalling of the transmission units in thereordering queue if some transmission units are not correctly received;start a reset timer associated with transmission units having a commondestination address and a common sequence number; determine that thereset timer has expired; and responsive to expiration of the resettimer, reset the value of sequence number for the next expectedtransmission unit and the upper boundary of a receiver window in themobile terminal to a predefined initial value.